The invention relates to ink-jet ink compositions suited for use in the printing of magnetic ink character recognition, or MICR, documents. More particularly, the invention relates to a process of printing such documents using a MICR-readable inkjet ink composition.
Inks suited for use in printing MICR-readable documents are known. Such inks are generally employed in the printing and preparation of security documents, or documents that require a secure feature, such as checks. Conventional ink-jet inks contain a dye or pigment, a solvent system, which may be aqueous or non-aqueous in nature, and may include a combination of solvents or a single solvent, and various other components, included to address specific problems relating to ink performance, such as toner flow characteristics, the ink drying out over time as it sits in the cartridge or when it is deposited on the nozzle during printing, particulate matter in the ink settling out of solution over time, etc. Some well known additives used to control these parameters include humectants, surfactants, dispersion aides, biocides, and others. The amount of additive and the type used are dictated predominantly by the print engine for which the ink is being prepared, the intended use of the ink-jet ink, and the effect, if any, that each component may have on the performance of each other component.
Of particular interest in this instance are those inks which contain a magnetic pigment or component in an amount sufficient to generate a magnetic signal strong enough to be MICR-readable. Such inks generally fall into the category of magnetic inks in general, and in the more specific sub-category of MICR-readable inks. Generally the ink is used to print all or a portion of a document, such as checks, bonds, security cards, etc. For example, most checks exhibit an identification code area, usually at the bottom of the check. The characters of this identification code are usually MICR encoded. The document may be printed with a combination of MICR-readable ink and conventional ink, or with just MICR-readable ink. The document thus printed is then exposed to an appropriate source or field of magnetization, at which time the magnetic particles become aligned as they accept and retain a magnetic signal. The document can then be authenticated by passing it through a reader device which detects the magnetic signal of the MICR imprinted characters, or “reads” the signal, in order to authenticate or validate the document. Of particular importance in the foregoing is the ability of the magnetic component of the ink to retain a sufficient charge such that the printed characters retain their readable characteristic and are easily detected by the detection device or reader. The magnetic charge retained by the pigment or magnetic component is known as “remanence”. As might be expected, this characteristic tends to increase with particle size and with the density of the coating of the magnetic pigment.
In the past, thermal ribbon printing mechanisms were used to generate MICR-readable characters or indicia. In this printing technique the particle size and density of the magnetic pigment or particulate was not a limiting factor because the magnetic component was retained on a ribbon substrate by a binder and/or wax material. Then, upon application of heat and pressure the magnetic ink was transferred to a substrate. However, the incorporation of such magnetic pigments or particulates into an aqueous, or a non-aqueous, liquid ink presents a new set of considerations. For example, the pigment, which had generally previously been used in the form of pigment or particulate matter of a larger size, and thus exhibited a correspondingly high density, is difficult to maintain in suspension or dispersion within a liquid ink composition. Consequently, it became necessary to reduce the particle size of the magnetic pigment or particulate. However, with a reduction in particle size came a corresponding reduction in magnetic charge or remanence. In addition to the foregoing, one wishing to prepare a liquid MICR inkjet ink must also take into consideration the fact that most, if not all, inkjet printers limit considerably the particle size of any particulate components of the ink, due to the very small size of the inkjet print head nozzle which expels the ink onto the substrate. Problems such as the foregoing required resolution before a suitable MICR-readable inkjet ink could be formulated.
These problems have been addressed in several different ways. For example, U.S. Ser. No. 10/186,492, assigned to our common assignee, discloses the use of a combination of surfactants, in conjunction with a very small particle size metal oxide component, to maintain a useful suspension or dispersion of the magnetic component within the ink composition. The ink disclosed in this application, while it contains a significant amount of metal oxide, nonetheless retains the same in suspension and is then suitable for MICR printing applications. Another means of achieving an ink-jet ink suitable for use in ink-jet printers, and also for generating MICR-readable print, is to coat the metal oxide with a specific hydrophilic coating to help retain the particulate metal oxide magnetic pigment in suspension.
The foregoing methods successfully achieve the desired result, i.e., an ink-jet ink with particulate matter small enough to be efficiently ejected through the ink-jet nozzle, and yet present in an amount sufficient to generate a strong enough signal that the printed document is MICR-readable. However, additional ink components are in each case necessary to this achievement. It has remained for the subject inventors to develop a printing method that achieves the same strong magnetic signal, suitable for MICR applications, and that does so with a reduced magnetic pigment or particulate loading and without any special additives to retain the particulates in suspension.